Magosi, the Waterveil, Rings of Brighthearth, and Argothian Elder

Prerequisites

• Magosi, the Waterveil on the battlefield
• Rings of Brighthearth on the battlefield
• Argothian Elder on the battlefield
• Argothian Elder does not have summoning sickness
• each turn available

Steps

1. Activate Magosi's second activated ability by tapping it and paying
2. Rings of Brighthearth triggers; choose not to pay for it
3. Resolve the Magosi ability, putting an eon counter on Magosi and skipping your next turn
4. Activate Argothian Elder by tapping it targeting Magosi and another land of your choice
5. Rings of Brighthearth triggers; choose not to pay for it
6. Activate Magosi's third activated ability by tapping it, removing an eon counter from it, and returning it to your hand
7. Rings of Brighthearth triggers; pay and copy the Magosi ability
8. Resolve both copies of the ability, cancelling out your skipped turn and taking an extra turn after this one
9. Play Magosi
10. Repeat each turn

Results

• Infinite turns